This invention relates generally to the field of control mechanisms for power tools, and more particularly to a combination stop for limiting the movement of a cutting tool carriage on a lathe.
Generally, in the machining of workpieces using a lathe, a carriage assembly carrying a cutting tool is driven, either manually or automatically, along a guide track, so that the cutting tool can machine a predetermined section of the workpiece. The final position of the carriage and therefore of the cutting tool, along the length of the workpiece, can be set in one of several ways. A common procedure is to fix a dial indicator, or similar gauge, at an appropriate location adjacent the path of the carriage, to monitor the indicator during the travel of the carriage and to terminate movement of the carriage when the desired reading is displayed on the indicator. However, such a procedure is inadequate for the precision machining of multiple pieces of the same dimension, because it is dependent on the skill of the individual operator to slow down and stop the lathe at the precise location time after time.
For such repetitive cuts, a more reliable method for providing a positive stop must be used. For this purpose it is known to secure a structurally rugged member to the frame of the lathe in such a way that the carriage, moving at its normal speed, can impinge on a portion of the member. The mass of the member is such that it can withstand the impact of the carriage without being deformed or otherwise damaged, and it is sufficiently anchored to the frame that it does not shift position when struck. Upon impinging on the essentially immovable member, the carriage stops at a well-defined position. Oftentimes the sudden stop produces a momentary disengagement of the driving means from the carriage to prevent needless damage. Because of the rugged nature of the member and its immovability, the carriage stops at the same precise location, workpiece after workpiece.
In many cases the impacted portion of the member may be continuously adjustable in position to vary the termination point of the cut on the workpiece. Often this adjustment has its own integral scale for example in the form of a micrometer or vernier, to allow changes of a precise amount. Alternatively, some stop members have multiple impact portions, each preset to a different length, which are rapidly interchangeable, for example via a rotatable turret, to define different termination points for different cutting operations on the workpiece. Typically these multiple preset portions require use of an external scale or gauge for precise setting. Such a procedure often is needlessly time consuming and costly.
Therefore it is an object of the present invention to provide a reliable stop for a lathe which combines an incrementally selectable stop assembly with an interacting continuously variable stop element to facilitate rapid and accurate determination of cutting tool stop positions.